​EI-Nino is a complex weather system that appears once every ___________ years, bringing drought, floods, and other weather extremes to different parts of the world including India.​

Correct option is A

The correct answer is (A) three to seven.

El Niño is a complex weather system that occurs roughly every three to seven years. It is a warming of the tropical Pacific that can cause drought, floods, and other weather extremes. 

Explanation

• El Niño is a warming of the tropical Pacific Ocean that occurs when trade winds weaken and warm water moves eastward. 
• It's linked to the Southern Oscillation, which is a change in atmospheric pressure between the Australian–East Asian region and the eastern tropical Pacific. 
• El Niño can impact weather in many places, including India, where it can lead to below-normal rainfall and droughts. 
• The name El Niño is Spanish for "the child" and refers to the baby Christ, as the current usually appears around Christmas.